1. Field of the Invention
This invention relates to printers and more particularly to a printer comprising a device for detecting a travel condition of an inkribbon.
2. Description of the Prior Art
Heretofore it has been the common practice to check a travel condition of an inkribbon for a printer by lightly urging a tension type detection member against the inkribbon stretched under tension across a carrier and detecting an amount of tension subjected to the inkribbon, thereby detecting a trouble induced in an inkribbon tranferring mechanism. That is, as shown in FIG. 1, a detection member a has one end supported by a carrier b and another free end urging a loop of inkribbon e located outside a ribbon cassette d outwardly by means of a spring c. In this case, if the detection member a is displaced in a direction of reducing the loop of inkribbon e inwardly against the action of spring c, the detection member a becomes engaged with a detection switch f secured to the carrier b so as to deliver an electrical signal therefrom, thereby detecting the trouble induced in the inkribbon transferring mechanism.
Such prior art devices, however, can only detect an abnormally large tension subjected to the inkribbon, so that it is impossible to detect troubles that tend to be induced even when the abnormally large tension is not subjected to the inkribbon, for example, a breakage of the inkribbon, separation of a joint between adjacent inkribbons, trouble induced in the inkribbon transferring mechanism, etc. In addition, such prior art device cannot detect trouble induced in the detection device itself and hence it is impossible to detect trouble of the inkribbon which is induced when the detection device is out of order.
As a result, the prior art device has had several drawbacks:
In the first place, the device could not detect the breakage of inkribbon or the separation of the joint between adjacent inkribbons, so that even when a printer functions to impact a desired letter or symbol with a record medium, the absence of the inkribbon results in no imprint on the record medium.
Secondly, whe an inkribbon transferring mechanism for feeding a long inkribbon for the purpose of alleviating the difference between concentrations of characters imprinted on the record medium malfunction and hence the inkribbon stops, such stopped condition of the inkribbon cannot be detected. As a result, a portion of the stopped inkribbon is located between a printer head and the record medium, so that the character imprint impacted on the record medium becomes gradually obscure such that the character imprint could not be deciphered and finally disappears. In addition, there is a risk of the inkribbon being broken by impacting the printer head and platen thereon.
Furthermore, the prior art device cannot detect a trouble induced in the printer head carrier.